Image data, which may be used to visualize an imaged examination object, is generated with the aid of modern imaging methods. The imaging methods are often based on the acquisition of x-ray radiation. During the visualization with the aid of x-ray radiation, x-ray radiation impinges on an examination object. The x-rays are absorbed to a different extent depending on the structural build of the examination object. The transmitted component of the x-ray radiation is captured on a projection surface or detector surface of an x-ray detector. The inner structures of the examination object, in particular the skeleton of a patient, may be deduced on the basis of the different local intensities of the x-ray radiation acquired at the projection surface of the x-ray detector. Here, bones absorb particularly large amounts of radiation such that little radiation arises at the corresponding points on the detector surface and these points are also only blackened a little in a pictorial representation. Therefore, skeleton parts appear bright in a pictorial representation while regions of the body that absorb little radiation, (e.g., soft tissue), appear dark.
However, x-ray radiation is not only absorbed in the examination object during the imaging with the aid of x-ray radiation; a significant component of the x-ray radiation is also scattered in the respective examination object itself, especially in the case of a thick examination object. The image contrast is reduced and hence image quality is impaired as a result of the occurrence of these scattered rays.
In order to reduce the described influence of the scattered radiation, a conventional imaging x-ray system also includes an anti-scatter grid for reducing the scattered radiation, in addition to an x-ray emitter with an x-ray source and an x-ray detector. A conventional anti-scatter grid, which is also referred to as anti-scatter grating, includes scattered radiation lamella with a large line number. The anti-scatter grid is arranged between the examination object and the x-ray detector in such a way that the radiation scattered by the examination object is absorbed by the scattered radiation lamellas. Such a grid may include lead or another strongly absorbing material and the regions between the grid structure includes a stabilizing, less absorbing material such as paper and aluminum.
There are also anti-scatter grids with cutouts between the grid structures. These anti-scatter grids are advantageous in that less radiation is absorbed by the anti-scatter grid as a result of the cutouts, as a result of which a lower patient dose emerges in the case of the same image quality. These grid structures, however, appear in the images acquired by the x-ray detectors in x-ray imaging when using such anti-scatter grids as a result of the very different absorption of the cutouts compared to the grid lamellas of the grid structures, the appearing grid structures, however, adversely affecting the image reproduction there. Conventionally, complex correction algorithms are used to eliminate these interfering images of the grid structures.
Another option for avoiding the imaging of the grid structures includes using a moving anti-scatter grid with a low line number. Moving the anti-scatter grid avoids spatially dependent differences of the x-ray intensity corresponding to the grid structures being imaged on the x-ray detector.
Alternatively, anti-scatter grids are also omitted and the resulting scattered radiation component in the imaging is subsequently removed by calculation on the basis of model considerations. Furthermore, it is also possible prior to imaging to calibrate the brightness variations or brightness differences caused on the x-ray detector by the grid and thus compensate these during the image evaluation.
Moreover, attempts are conventionally made to reduce the interfering imaging of the grid structures with the aid of suitable grid geometries. This is possible, in particular, by using grids with a very high number of grid lamellas per millimeter.